This invention relates to a driveshaft for a snowmobile. In particular, this invention relates to a driveshaft having improved torque transfer characteristics and reduced weight.
Snowmobiles are becoming increasingly popular. Examples of known snowmobiles are described in U.S. Pat. Nos. 4,987,965; 5,660,245; 5,667,031; and 5,904,217. The increasing popularity of snowmobiles increases competition between manufacturers. As a result, snowmobiles manufacturers have been increasing the horsepower of the engines which increases the top speed of the vehicles in order to make the vehicles more marketable.
Typically, a snowmobile has a drive track positioned beneath a frame assembly. A transmission is provided to receive power from the engine. The power is then transferred to the drive track via a rotatably mounted driveshaft. A pair of sprockets is mounted on the driveshaft in order to transfer power to the drive track.
Heretofore, driveshafts for snowmobiles have been made from solid hot rolled steel bar stock. The bar stock has a hexagonal cross section. The sprockets are then mounted on the bar stock and fixed thereon.
Current driveshafts are able to effectively transfer power to the track. However, current driveshafts are also subjected to shock loading especially when the snowmobile travels over rough terrain at high rates of speed. The shock loads cause shaft bending which damages the supporting bearing housings and destroys the shaft to sprocket interface. Current driveshafts are able to sustain at most 50 repetitive shock loads of 1500 ft-lbs before the driveshaft or bearing is permanently deformed or damaged.
Thus, there exist a need in the production of snowmobiles for a driveshaft capable of transferring increasingly amounts of torque, having a reduced weight, while being capable of withstanding severe shock loads without significant deformation.
The disadvantages of the prior art may be overcome by providing a hollow driveshaft having a series of longitudinally extending splines which frictionally receives a pair of sprockets.
It is desirable to provide a hollow driveshaft having an increased diameter to improve bending stiffness and reduce stress therein.
According to one aspect of the invention, there is provided a driveshaft for a snowmobile that has an elongated hollow tube having a longitudinal extent. The tube has a series of circumferentially spaced longitudinally extending splines. Both ends of the tube each have an insert for journal mounting the tube. Sprockets are mounted on the tube in a spaced relation. Each of the sprockets has an inner hub which has an inner circumferential surface contoured to complementarily engage with the tube in a frictional fit.